Transparent conductive laminate and touch panel therewith

ABSTRACT

A transparent conductive laminate of the invention comprises: a transparent film substrate; a transparent conductive thin film provided on one side of the transparent film substrate; and a transparent base substrate bonded to another side of the transparent film substrate with a transparent pressure-sensitive adhesive layer interposed therebetween, wherein the transparent conductive thin film comprises a first transparent conductive thin film made of an indium-tin complex oxide in which SnO 2 /(SnO 2 +In 2 O 3 ) is from 2 to 6% by weight and a second transparent conductive thin film made of an indium-tin complex oxide in which SnO 2 /(SnO 2 +In 2 O 3 ) is more than 6% by weight and not more than 20% by weight, the first and second transparent conductive thin films are formed in this order from the transparent film substrate side, the thickness t 1  of the first transparent conductive thin film and the thickness t 2  of the second transparent conductive thin film have the following relationships: ( 1 ) t 1  is from 10 to 30 nm; ( 2 ) t 2  is from 5 to 20 nm; and ( 3 ) the sum of t 1  and t 2  is from 20 to 35 nm, the first transparent conductive thin film and the second transparent conductive thin film are both crystalline films, and the transparent base substrate is a transparent laminated base substrate comprising at least two transparent base films laminated to one another with a transparent pressure-sensitive adhesive layer interposed therebetween. The transparent conductive laminate has satisfactory reliability at high temperature and high humidity for touch panels and also has pen input durability and surface pressure durability.

TECHNICAL FIELD

The present invention relates to a transparent conductive laminateincluding a film substrate and a conductive thin film provided on thefilm substrate and having transparency in the visible light range andalso relates to a touch panel therewith. The transparent conductivelaminate of the invention may be used for transparent electrodes indisplay systems such as liquid crystal displays and electroluminescencedisplays and touch panels and also used for electromagnetic waveshielding or prevention of static charge of transparent products.

BACKGROUND ART

Touch panels can be classified according to the position detectionmethod into an optical type, an ultrasonic type, a capacitive type, aresistive film type, and the like. In particular, the resistive filmtype has a relatively simple structure and thus is cost-effective sothat it has come into wide use in recent years. For example, resistivefilm type touch panels are used for automatic teller machines (ATMs) inbanks and for display panels of transportation ticket machines and thelike.

The resistive film type touch panels are configured to include a pair oftransparent conductive films arranged opposite to each other with aspacer interposed therebetween, in which an electric current is allowedto flow through the upper transparent conductive film, while the voltageat the lower transparent conductive film is measured. When the uppertransparent conductive film is brought into contact with the lowertransparent conductive film by pressing with a finger, a pen or thelike, the electric current flows through the contact portion so that theposition of the contact portion is detected.

Conventionally, the so-called conductive glass is well known as such atransparent conductive film, which comprises a glass and an indium oxidethin film formed thereon. Since the conductive glass has a glasssubstrate, however, it has low flexibility or workability, and cannot beused for certain purposes in some cases.

In recent years, therefore, transparent conductive films using varioustypes of plastic films such as polyethylene terephthalate films as theirsubstrate have been used, because of their advantages such as goodimpact resistance and light weight as well as flexibility andworkability. However, such conventional transparent conductive films notonly have the problem of low transparency due to high light reflectanceof the thin film surface but also have low scratch resistance or lowbending resistance with respect to the conductive thin film so that theyhave problems in which they can get scratched to have an increasedelectrical resistance or suffer from disconnection during use. Theconventional transparent conductive films also have low environmentalresistance and thus have a problem in which the surface resistance caneasily change in a high-temperature, high-humidity atmosphere so thatthe reliability can be poor at high temperature and high humidity. Inrecent years, the market for touch panels to be installed in outdoorsmartphones, car navigation systems and the like is expanding, andtherefore, there is a strong demand for improvements in thehigh-temperature, high-humidity reliability of touch panels.

To solve these problems, attempts have been made to improvetransparency, durability and the like with a two-layer structure oftransparent conductive thin film formed on a film substrate. Forexample, it is proposed that a first transparent conductive thin filmwith a small crystal particle size is formed on a film substrate, and asecond transparent conductive thin film with a large crystal particlesize is formed thereon, so that transparency, pressure resistance,durability, and the like can be improved and curling properties and thelike can be reduced (Patent Literature 1: JP-A No. 2003-263925). It isalso proposed that first and second transparent conductive thin filmswhich differ in oxygen content and nitrogen content are formed on a filmsubstrate so that pen input durability can be improved (PatentLiterature 2: JP-A No. 2003-151358). However, the techniques disclosedin these literatures cannot achieve satisfactory reliability at hightemperature and high humidity.

It is also proposed that a two-layer structure of transparent conductivethin film is formed which comprises an indium-tin complex oxide thinfilm with a low SnO₂ content (3 to 8% by weight) provided on a filmsubstrate and another indium-tin complex oxide thin film with a highSnO₂ content (10 to 30% by weight) provided thereon, so thattransparency can be improved and that a rise in surface resistance canbe suppressed in an annealing step for processing a touch panel or in adrying step for printing silver electrodes or spacers (Patent Literature2: JP-A No. 10-49306). However, a transparent touch panel electrodecomposed of the transparent conductive thin films disclosed in PatentLiterature 3 does not have sufficient mechanical strength and thuscannot achieve satisfactory pen input durability.

By the way, in recent years, the market for touch panels to be installedin smartphones, personal digital assistances (PDAs), game computers, andthe like is expanding, and the frame part of touch panels becomesnarrower. This increases the opportunity to push touch panels withfingers so that not only requirements for pen input durability but alsorequirements for surface pressure durability is satisfied. However, thetechniques disclosed in the patent literatures cannot achievesatisfactory pen input durability and thus can never achievesatisfactory surface pressure durability.

DISCLOSURE OF INVENTION

The invention has been made in view of the above problems. It istherefore an object of the invention to provide a transparent conductivelaminate that includes a transparent film substrate, a transparentconductive thin film provided on one side of the transparent filmsubstrate, and a transparent base substrate bonded to the other side ofthe transparent film substrate with a transparent pressure-sensitiveadhesive layer interposed therebetween, and has satisfactory reliabilityat high temperature and high humidity for touch panels and also has peninput durability and surface pressure durability. It is another objectof the invention to provide a touch panel including such a transparentconductive laminate.

In order to solve the above problems, the inventors have made activeinvestigations on transparent conductive laminates and touch panelstherewith. As a result, it has been found that the objects can beachieved using the features described below, and the invention has beencompleted.

The present invention relates to a transparent conductive laminate,comprising:

a transparent film substrate;

a transparent conductive thin film provided on one side of thetransparent film substrate; and

a transparent base substrate bonded to another side of the transparentfilm substrate with a transparent pressure-sensitive adhesive layerinterposed therebetween, wherein

the transparent conductive thin film comprises a first transparentconductive thin film made of an indium-tin complex oxide in whichSnO₂/(SnO₂+In₂O₃) is from 2 to 6% by weight and a second transparentconductive thin film made of an indium-tin complex oxide in whichSnO₂/(SnO₂+In₂O₃) is more than 6% by weight and not more than 20% byweight,

the first and second transparent conductive thin films are formed inthis order from the transparent film substrate side,

the thickness t₁ of the first transparent conductive thin film and thethickness t₂ of the second transparent conductive thin film have thefollowing relationships:

(1) t₁ is from 10 to 30 nm;(2) t₂ is from 5 to 20 nm; and(3) the sum of t₁ and t₂ is from 20 to 35 nm,

the first transparent conductive thin film and the second transparentconductive thin film are both crystalline films, and

the transparent base substrate is a transparent laminated base substratecomprising at least two transparent base films laminated to one anotherwith a transparent pressure-sensitive adhesive layer interposedtherebetween.

In the transparent conductive laminate, the transparent conductive thinfilm is preferably formed through a transparent dielectric thin filmfrom on the film substrate.

In the transparent conductive laminate, the transparent base substratemay have a resin layer provided on the outer surface thereof.

The present invention also relates to a touch panel, comprising theabove transparent conductive laminate.

The transparent conductive thin film disclosed in Patent Literature 3can be used to form a transparent touch panel electrode. In such a case,it may be considered that a crystalline film is formed in order toincrease the mechanical strength and to retain surface pressuredurability as well as pen input durability. Patent Literature 3discloses a number of examples in which the SnO₂ content of the secondtransparent conductive thin film is set at 30% by weight. However, thethin film of such examples cannot be successfully crystallized by a heattreatment at a low temperature of 150° C. or less, which is acceptableto the film substrate. Patent Literature 3 also discloses a number ofexamples in which the SnO₂ content of the first transparent conductivethin film is set at 8% by weight. However, the thin film of suchexamples cannot be crystallized, unless the time of the heat treatmentat the low temperature is considerably long. On the other hand, PatentLiterature 3 discloses a number of examples in which the thickness ofthe second transparent conductive thin film with a high SnO₂ content isset at 30 angstroms (namely 3 nm). However, the thin film of suchexamples is hardly expected to have high-temperature, high-humidityreliability desired for touch panels.

According to the invention, a two-layer structure of transparentconductive thin film is formed on a transparent film substrate,similarly to Patent Literature 3, and such a two-layer structurecomprises a first transparent conductive thin film of an indium-tincomplex oxide with a relatively low SnO₂ content formed on the filmsubstrate and a second transparent conductive thin film of an indium-tincomplex oxide with a relatively high SnO₂ content formed on the firsttransparent conductive thin film. However, the SnO₂ content of each ofthe first and second transparent conductive thin films is limited withina relatively low range, as compared with that in Patent Literature 3. Inaddition, the thickness of each of the first and second transparentconductive thin films and the sum of the thicknesses of both thin filmsare each set in a specific range. According to the invention, the SnO₂content of each of the first and second transparent conductive thinfilms and the thickness of each thin film are controlled as describedabove so that these thin films can be sufficiently crystallized by aheat treatment at a low temperature of 150° C. or less, which isacceptable to the film substrate, and thus the transparent conductivethin films can be provided with a crystalline film structure. Accordingto the invention, therefore, the crystalline structure of thetransparent conductive thin films can provide satisfactory surfacepressure durability in addition to transparency and pen input durabilityand also allows the production of transparent conductive thin films withhigh reliability at high temperature and high humidity.

According to the invention, the structure of the transparent conductivelaminate includes a transparent laminated base substrate that isprovided on the transparent conductive thin film-free side of thetransparent film substrate and comprises at least two transparent basefilms laminated with a transparent pressure-sensitive adhesive layerinterposed therebetween. Such a structure can improve not only pen inputdurability but also surface pressure durability, when the transparentconductive laminate is used in touch panels.

If the transparent conductive thin film is formed on the film substratewith a transparent dielectric thin film interposed therebetween, the peninput durability and the surface pressure durability can be furtherimproved. Specifically, the dielectric thin film is particularlyeffective as an undercoat layer for the transparent conductive thin filmso that it can improve the durability to in-plane pressure.

According to the invention, therefore, the SnO₂ content of each of thefirst and second transparent conductive thin films composed of anindium-tin complex oxide is limited in a specific range, and thethickness of each thin film and the sum of the thicknesses of both thinfilms are also limited in a specific range, so that the thin films canbe crystallized by a heat treatment at low temperature for shortperiods. The crystalline structure of the first and second transparentconductive thin films and the transparent laminated base substrateprovided on the transparent conductive thin film-free side of thetransparent film substrate can sufficiently provide transparency, peninput durability and surface pressure durability and also allows theproduction of a transparent conductive laminate with high reliability athigh temperature and high humidity. When such a transparent conductivelaminate is used as a transparent electrode, a touch panel with highreliability required for smartphones or car navigation systems can beprovided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view showing a transparentconductive laminate according to an embodiment of the invention;

FIG. 2 is a schematic cross-sectional view showing a transparentconductive laminate according to another embodiment of the invention;

FIG. 3 is a schematic cross-sectional view showing a touch panelaccording to a further embodiment of the invention;

FIG. 4 is a schematic cross-sectional view for illustrating a surfacepressure durability test of touch panels according to examples of theinvention; and

FIG. 5 is a graph showing the relationship between the voltage value ata touch panel obtained in example 1 and the measurement point.

BEST MODE FOR CARRYING OUT THE INVENTION

Some embodiments of the invention are described below with reference tothe drawings, in which some portions unnecessary for explanation areomitted, and some portions are illustrated in an enlarged, reduced ormodified form for easy understanding.

FIGS. 1 and 2 are schematic cross-sectional views each showing anexample of the transparent conductive laminate according to anembodiment of the invention. In FIG. 1, a transparent conductivelaminate A has a structure including a transparent film substrate 1, atransparent conductive thin film 2 provided on one side of the filmsubstrate 1, and a transparent laminated base substrate 3 bonded to theother side of the film substrate 1 with a pressure-sensitive adhesivelayer 41 interposed therebetween. In this structure, the transparentconductive thin film 2 includes a first transparent conductive thin film21 and a second transparent conductive thin film 22 that are formed inthis order from the film substrate 1 side. The transparent laminatedbase substrate 3 includes a transparent base film 31 and anothertransparent base film 32 that are laminated with a transparentpressure-sensitive adhesive layer 42 interposed therebetween. While FIG.1 illustrates a case where two transparent base films are laminated, twoor more transparent base films may be laminated, and specifically three,four, five, or more transparent base films may be laminated. Such astructure can further increase in-plane durability. FIG. 1 shows a casewhere a hard coat layer (resin layer) 6 is further provided on the outersurface of the transparent laminated base substrate 3. FIG. 2 shows acase where in the structure of FIG. 1, the transparent conductive thinfilm 2 is provided on the side of the film substrate 1 with atransparent dielectric thin film 5 interposed therebetween.

There is no particular limitation to the film substrate 1, and varioustypes of plastic films having transparency may be used. Examples of thematerial for the film substrate 1 include polyester resins, acetateresins, polyethersulfone resins, polycarbonate resins, polyamide resins,polyimide resins, polyolefin resins, (meth)acrylic resins, polyvinylchloride resins, polyvinylidene chloride resins, polystyrene resins,polyvinyl alcohol resins, polyarylate resins, and polyphenylene sulfideresins. In particular, polyester resins, polycarbonate resins, andpolyolefin resins are preferred.

Examples thereof also include polymer films as disclosed in JP-A No.2001-343529 (WO01/37007) and a resin composition that contains (A) athermoplastic resin having a side chain of a substituted and/orunsubstituted imide group and (B) a thermoplastic resin having a sidechain of substituted and/or unsubstituted phenyl and nitrile groups.Specifically, a polymer film of a resin composition containing analternating copolymer made of isobutylene and N-methylmaleimide, and anacrylonitrile-styrene copolymer may be used.

The thickness of the film substrate 1 is preferably in the range of 2 to200 μm, more preferably in the range of 2 to 100 μm. If the thickness ofthe film substrate 1 is less than 2 μm, the film substrate 1 can haveinsufficient mechanical strength so that it can be difficult to use thefilm substrate 1 in the form of a roll in the process of continuouslyforming the conductive thin film 2, the dielectric thin film 5 and thepressure-sensitive adhesive layer 41 in some cases. If the thicknessexceeds 200 μm, it can be impossible to improve the scratch resistanceof the conductive thin film 2 or the tap properties thereof for touchpanels based on the cushion effect of the pressure-sensitive adhesivelayer 41 in some cases.

The surface of the film substrate 1 may be previously subject tosputtering, corona discharge treatment, flame treatment, ultravioletirradiation, electron beam irradiation, chemical treatment, etchingtreatment such as oxidation, or undercoating treatment such that theadhesion of the conductive thin film 2 or the dielectric thin film 5formed thereon to the film substrate 1 can be improved. If necessary,the film substrate may also be subjected to dust removing or cleaning bysolvent cleaning, ultrasonic cleaning or the like, before the conductivethin film 2 or the dielectric thin film 5 is formed.

The dielectric thin film 5 shown in FIG. 2 may be made of an inorganicmaterial, an organic material or a mixture of inorganic and organicmaterials. For example, such an inorganic material as SiO₂, MgF₂ orAl₂O₃ is preferably used. Examples of the organic material includeacrylic resins, urethane resins, melamine resins, alkyd resins, andsiloxane polymers. In particular, a thermosetting resin comprising amixture of a melamine resin, an alkyd resin and an organosilanecondensate is preferably used as the organic material.

The dielectric thin film 5 may be formed with any of the above materialsby a dry process such as vacuum deposition, sputtering, and ion platingor by a wet process (coating method). The dielectric thin film 5 may bea single layer or composed of two or more layers. In general, thethickness of the dielectric thin film 5 (the thickness of each layer inthe case of multilayers) is preferably from about 1 to 300 nm.

The first and second transparent conductive thin films 21 and 22 of anindium-tin complex oxide (indium tin oxide) are formed on the filmsubstrate 1 by any known thin film-forming method such as vacuumdeposition, sputtering and ion plating. While any appropriate materialmay be selected to form such a thin film, depending on the thinfilm-forming method, in general, a sintered material of indium oxide andtin oxide is preferably used. In such a thin film-forming method asreactive sputtering, the thin film may also be formed with indium metaland tin metal, while both metals are oxidized.

When such a transparent conductive thin film is formed, ratio betweenamounts of the thin film-forming materials, indium oxide and tin oxide(or the ratio between the amounts of indium metal and tin metal) isselected, and indium-tin complex oxides different in SnO₂ content areformed for the first transparent conductive thin film, which is lowerlayer, and the second transparent conductive thin film, which is upperlayer, respectively. Specifically, according to the invention, the firsttransparent conductive thin film is made of an indium-tin complex oxidein which SnO₂/(SnO₂+In₂O₃) is from 2 to 6% by weight, particularlypreferably from 3 to 5% by weight, and the second transparent conductivethin film is made of an indium-tin complex oxide in whichSnO₂/(SnO₂+In₂O₃) is more than 6% by weight and not more than 20% byweight, particularly preferably from 10 to 15% by weight.

If the SnO₂ content of each of the first and second transparentconductive thin films is set in the above specified range, it ispossible to form a transparent conductive thin film that can becrystallized by a heat treatment at low temperature for short periodsand has not only transparency and pen input durability but also goodsurface pressure durability and high reliability at high temperature. Incontrast, if the content of SnO₂ is less than 2% by weight in the firsttransparent conductive thin film or 6% by weight or less in the secondtransparent conductive thin film, sufficient reliability cannot beachieved at high temperature or high humidity, and if the content ofSnO₂ is more than 6% by weight in the first transparent conductive thinfilm or more than 20% by weight in the second transparent conductivethin film, the heat treatment for crystallization can take a long time,or crystallization itself can be difficult.

In the invention, it is also important to set the thickness of each ofthe first and second transparent conductive thin films in a specificrange or to set the sum of the thicknesses in a specific range.Specifically, the thickness t₁ of the first transparent conductive thinfilm and the thickness t₂ of the second transparent conductive thin filmneed to have the following relationships:

(1) t₁ is from 10 to 30 nm, preferably from 10 to 20 nm;(2) t₂ is from 5 to 20 nm, preferably from 5 to 15 nm; and(3) the sum of t₁ and t₂ (t₁+t₂) is from 20 to 35 nm, preferably from 25to 30 nm. Only if these thickness relationships are established, it ispossible to form a transparent conductive thin film that can becrystallized by a heat treatment at low temperature for short periodsand has not only transparency and pen input durability but also goodsurface pressure durability and high reliability at high temperature andhigh humidity.

In contrast, if the thickness t₁ of the first transparent conductivethin film is less than 10 nm or if the thickness t₂ of the secondtransparent conductive thin film is less than 5 nm, it is difficult toform continuous films, and sufficient reliability cannot be achieved athigh temperature or high humidity. If the thickness t₁ of the firsttransparent conductive thin film is more than 30 nm or if the thicknesst₂ of the second transparent conductive thin film is more than 20 nm,the surface resistance value can be too low, or the transparency can bereduced. If the sum of the thickness t₁ of the first transparentconductive thin film and the thickness t₂ of the second transparentconductive thin film is less than 20 nm, sufficient reliability cannotbe achieved at high temperature or high humidity, or the surfaceresistance value can be high. If the sum exceeds 35 nm, crystallizationcan be difficult, or the transparency can be reduced.

According to the invention, the first and second transparent conductivethin films each with a specific SnO₂ content and a specific thicknessare sequentially formed and then subjected to an appropriate heattreatment to be both crystallized and turned into a crystalline film.The heat treatment may be performed using a heating system such as aninfrared heater and a circulating hot air oven according to knownmethods. In this process, a temperature of the heat treatment may be150° C. or less, which is acceptable to the film substrate, andcrystallization can be sufficiently achieved by the heat treatment atsuch a low temperature for a short time period according to theinvention. Specifically, good crystalline films can be formed by theheat treatment at 150° C. for a time period of at most 2 hours.

The other side of the film substrate 1 provided with the conductive thinfilm 2 (composed of the first and second transparent conductive thinfilms 21 and 22) is bonded to the transparent laminated base substrate 3with the transparent pressure-sensitive adhesive layer 41 interposedtherebetween. The transparent laminated base substrate 3 has a compositestructure comprising at least two transparent base films bonded to eachother with a transparent pressure-sensitive adhesive layer. Thecomposite structure can improve the pen input durability and also thesurface pressure durability.

In general, a thickness of the transparent laminated base substrate 3 ispreferably controlled to be from 90 to 300 μm, more preferably from 100to 250 μm. The thickness of each base film constituting the transparentlaminated base substrate 3 may be from 10 to 200 μm, preferably from 20to 150 μm, and may be controlled such that the total thickness of thetransparent laminated base substrate 3 including these base films andthe transparent pressure-sensitive adhesive layer(s) can fall within theabove range. Examples of the material for the base film include thosefor the film substrate 1.

The film substrate 1 and the transparent laminated base substrate 3 maybe bonded by a process including the steps of forming thepressure-sensitive adhesive layer 41 on the transparent laminated basesubstrate 3 side and bonding the film substrate 1 thereto or by aprocess including the steps of forming the pressure-sensitive adhesivelayer 41 contrarily on the film substrate 1 side and bonding thetransparent laminated base substrate 3 thereto. The latter process ismore advantageous in view of productivity, because it enables continuousproduction of the pressure-sensitive adhesive layer 41 with the filmsubstrate 1 in the form of a roll. Alternatively, the transparentlaminated base substrate 3 may be formed on the film substrate 1 bysequentially laminating the base films 31 and 32 with thepressure-sensitive adhesive layers 41 and 42. The transparentpressure-sensitive adhesive layer (the pressure-sensitive adhesive layer42 in FIG. 1 or 2) for use in laminating the base films may be made ofthe same material as the transparent pressure-sensitive adhesive layer41 described below.

Any transparent pressure-sensitive adhesive may be used for thepressure-sensitive adhesive layer 41 without limitation. For example,the pressure-sensitive adhesive may be appropriately selected fromadhesives based on polymers such as acrylic polymers, silicone polymers,polyester, polyurethane, polyamide, polyvinyl ether, vinyl acetate-vinylchloride copolymers, modified polyolefins, epoxy polymers,fluoropolymers, and rubbers such as natural rubbers and syntheticrubbers. In particular, acrylic pressure-sensitive adhesives arepreferably used, because they have good optical transparency and goodweather or heat resistance and exhibit suitable wettability and adhesionproperties such as cohesiveness and adhesiveness.

The anchoring strength can be improved using an appropriatepressure-sensitive adhesive primer, depending on the type of thepressure-sensitive adhesive as a material for forming thepressure-sensitive adhesive layer 41. In the case of using such apressure-sensitive adhesive, therefore, a certain pressure-sensitiveadhesive primer is preferably used.

The pressure-sensitive adhesive primer may be of any type as long as itcan improve the anchoring strength of the pressure-sensitive adhesive.For example, the pressure-sensitive adhesive primer that may be used isa so-called coupling agent such as a silane coupling agent having ahydrolyzable alkoxysilyl group and a reactive functional group such asamino, vinyl, epoxy, mercapto, and chloro in the same molecule; atitanate coupling agent having an organic functional group and atitanium-containing hydrolyzable hydrophilic group in the same molecule;and an aluminate coupling agent having an organic functional group andan aluminum-containing hydrolyzable hydrophilic group in the samemolecule; or a resin having an organic reactive group, such as an epoxyresin, an isocyanate resin, a urethane resin, and an ester urethaneresin. In particular, a silane coupling agent-containing layer ispreferred, because it is easy to handle industrially.

The pressure-sensitive adhesive layer 41 may contain a crosslinkingagent depending on the base polymer. If necessary, thepressure-sensitive adhesive layer 41 may also contain appropriateadditives such as natural or synthetic resins, glass fibers or beads, orfillers comprising metal powder or any other inorganic powder, pigments,colorants, and antioxidants. The pressure-sensitive adhesive layer 41may also contain transparent fine particles so as to have lightdiffusing ability.

The transparent fine particles to be used may be one or more types ofappropriate conductive inorganic fine particles of silica, calciumoxide, alumina, titania, zirconia, tin oxide, indium oxide, cadmiumoxide, antimony oxide, or the like with an average particle size of 0.5to 20 μm or one or more types of appropriate crosslinked oruncrosslinked organic fine particles of an appropriate polymer such aspoly(methyl methacrylate) and polyurethane with an average particle sizeof 0.5 to 20 μm.

The pressure-sensitive adhesive layer 41 is generally formed using apressure-sensitive adhesive solution with a solids content of about 10to 50% by weight, in which a base polymer or a composition thereof isdissolved or dispersed in a solvent. An organic solvent such as tolueneand ethyl acetate, water, or any other solvent may be appropriatelyselected depending on the type of the pressure-sensitive adhesive andused as the above solvent.

After the bonding of the transparent laminated base substrate 3, thepressure-sensitive adhesive layer 41 has a cushion effect and thus canfunction to improve the scratch resistance of the conductive thin filmformed on one side of the film substrate 1 or to improve the tapproperties thereof for touch panels, such as so called pen inputdurability and surface pressure durability. In terms of performing thisfunction better, it is preferred that the elastic modulus of thepressure-sensitive adhesive layer 41 is set in the range of 1 to 100N/cm² and that its thickness is set at 1 μm or more, generally in therange of 5 to 100 μm.

If the elastic modulus is less than 1 N/cm², the pressure-sensitiveadhesive layer 41 can be inelastic so that the pressure-sensitiveadhesive layer can easily deform by pressing to make the film substrate1 irregular and further to make the conductive thin film 2 irregular. Ifthe elastic modulus is less than 1 N/cm², the pressure-sensitiveadhesive can be easily squeezed out of the cut section, and the effectof improving the scratch resistance of the conductive thin film 2 orimproving the tap properties of the thin film 2 for touch panels can bereduced. If the elastic modulus is more than 100 N/cm², thepressure-sensitive adhesive layer 41 can be hard, and the cushion effectcannot be expected, so that the scratch resistance of the conductivethin film 2 or the pen input durability and surface pressure durabilityof the thin film 2 for touch panels tends to be difficult to beimproved.

If the thickness of the pressure-sensitive adhesive layer 41 is lessthan 1 μm, the cushion effect also cannot be expected so that thescratch resistance of the conductive thin film 2 or the pen inputdurability and surface pressure durability of the thin film 2 for touchpanels tends to be difficult to be improved. If it is too thick, it canreduce the transparency, or it can be difficult to obtain good resultson the formation of the pressure-sensitive adhesive layer 41, thebonding workability of the transparent laminated base substrate 3, andthe cost.

The transparent laminated base substrate 3 bonded through thepressure-sensitive adhesive layer 41 as described above imparts goodmechanical strength to the film substrate 1 and contributes to not onlythe pen input durability and the surface pressure durability but alsothe prevention of curling.

The pressure-sensitive adhesive layer 41 may be transferred using aseparator. In such a case, for example, the separator to be used may bea laminate of a polyester film of a migration-preventing layer and/or arelease layer, which is provided on a polyester film side to be bondedto the pressure-sensitive adhesive layer 41.

The total thickness of the separator is preferably 30 μm or more, morepreferably in the range of 75 to 100 μm. This is to prevent deformationof the pressure-sensitive adhesive layer 41 (dents) in a case where thepressure-sensitive adhesive layer 41 is formed and then stored in theform of a roll, in which the deformation (dents) can be expected to becaused by foreign particles or the like intruding between portions ofthe rolled layer.

The migration-preventing layer may be made of an appropriate materialfor preventing migration of migrant components in the polyester film,particularly for preventing migration of low molecular weight oligomercomponents in the polyester. An inorganic or organic material or acomposite of inorganic and organic materials may be used as a materialfor forming the migration-preventing layer. The thickness of themigration-preventing layer may be set in the range of 0.01 to 20 μm asneeded. The migration-preventing layer may be formed by any method suchas coating, spraying, spin coating, and in-line coating. Vacuumdeposition, sputtering, ion plating, spray thermal decomposition,chemical plating, electroplating, or the like may also be used.

The release layer may be made of an appropriate release agent such as asilicone release agent, a long-chain alkyl release agent, afluorochemical release agent, and a molybdenum sulfide release agent.The thickness of the release layer may be set as appropriate in view ofthe release effect. In general, the thickness is preferably 20 μm orless, more preferably in the range of 0.01 to 10 μm, particularlypreferably in the range of 0.1 to 5 μm, in view of handleability such asflexibility.

An ionizing radiation-curable resin such as an acrylic resin, a urethaneresin, a melamine resin, and an epoxy resin or a mixture of the aboveresin and aluminum oxide, silicon dioxide, mica, or the like may be usedin the coating, spraying, spin coating, or in-line coating method. Whenthe vacuum deposition, sputtering, ion plating, spray thermaldecomposition, chemical plating, or electroplating method is used, ametal such as gold, silver, platinum, palladium, copper, aluminum,nickel, chromium, titanium, iron, cobalt, or tin or an oxide of an alloythereof or any other metal compounds such as metal iodides may be used.

If necessary, an antiglare or antireflection layer for improvingvisibility or a hard coat layer (resin layer) 6 for protecting the outersurface may be formed on the outer surface of the transparent laminatedbase substrate 3 (on the side opposite to the pressure-sensitiveadhesive layer 41). The antiglare layer or the antireflection layer mayalso be formed on the hard coat layer 6 provided on the transparentlaminated base substrate 3. For example, the hard coat layer 6 ispreferably made of a cured coating film of a curable resin such as amelamine resin, a urethane resin, an alkyd resin, an acrylic resin, anda silicone resin.

For example, the material to be used to form the antiglare layer may be,but not limited to, an ionizing radiation-curable resin, a thermosettingresin, a thermoplastic resin, or the like. The thickness of theantiglare layer is preferably from 0.1 to 30 μm. If the thickness isless than 0.1 μm, there can be an apprehension of insufficient hardness.If the thickness is more than 30 μm, the antiglare layer can be crackedin some cases, or the whole of the transparent laminated base substrate3 coated with the antiglare layer can curl in some cases.

The antireflection layer may be formed on the hard coat layer 6. Lightincident on an object undergoes reflection on the interface, absorptionand scattering in the interior and any other phenomena until it goesthrough the object and reaches the back side. Light reflection at theinterface between air and the transparent laminated base substrate 3 orthe hard coat layer 6 is one of the factors behind the reduction invisibility of the image on a display equipped with a touch panel. Amethod for reducing the surface reflection includes laminating a thinfilm with strictly controlled thickness and refractive index on thesurface of the hard coat layer 6 such that an antireflection functioncan be produced by allowing different phases of incident light andreflected light to cancel each other out based on interference of light.

When the antireflection layer is designed based on interference oflight, the interference effect can be enhanced by increasing thedifference between the refractive indices of the antireflection layerand the hard coat layer 6. Two to five thin optical films (each withstrictly controlled thickness and refractive index) may be stacked onthe substrate to form an antireflection multilayer. In such a case,components with different refractive indices are generally used to forma plurality of layers with a certain thickness, so that theantireflection layer can be optically designed at a higher degree offreedom, the antireflection effect can be enhanced, and it may bepossible to make the spectral reflection characteristics flat in thevisible light range. Since each layer of the thin optical film isrequired to be precise in thickness, a dry process such as vacuumdeposition, sputtering, and CVD is generally used to form each layer.

The antireflection layer may use titanium oxide, zirconium oxide,silicon oxide, magnesium fluoride, or the like. In order to produce amore significant antireflection function, a laminate of a titanium oxidelayer(s) and a silicon oxide layer(s) is preferably used. Such alaminate is preferably a two-layer laminate comprising ahigh-refractive-index titanium oxide layer (refractive index: about1.8), which is formed on the hard coat layer 6, and alow-refractive-index silicon oxide layer (refractive index: about 1.45),which is formed on the titanium oxide layer. Also preferred is afour-layer laminate which comprises the two-layer laminate and atitanium oxide layer and a silicon oxide layer formed in this order onthe two-layer laminate. The antireflection layer of such a two- orfour-layer laminate can evenly reduce reflection over the visible lightwavelength range (380 to 780 nm).

The antireflection effect can also be produced by laminating a thinmonolayer optical film on the transparent laminated base substrate 3 orthe hard coat layer 6. In the design of the single antireflection layer,the difference between the refractive indices of the antireflectionlayer and the hard coat layer should be large for the maximumantireflection function. Concerning the thickness (d) and refractiveindex (n) of the antireflection layer and the wavelength (λ) of incidentlight, the relation nd=λ/4 can be established. If the refractive indexof the antireflection layer is lower than that of the substrate, itsreflectance can be minimal under the conditions that the relation isestablished. For example, if the refractive index of the antireflectionlayer is 1.45, the antireflection layer with a thickness of 95 nm canhave a minimum reflectance at a wavelength of 550 nm with respect to anincident beam of visible light.

The antireflection function is produced in the visible light wavelengthrange of 380 to 780 nm, and the visibility is particularly high in thewavelength range of 450 to 650 nm. The antireflection layer is generallydesigned to have a minimum reflectance at 550 nm, the center wavelengthof the range.

In the design of a single antireflection layer, its thickness accuracymay be less strict than that of the antireflection multilayer and may bein the range of ±10% with respect to the design thickness. In a casewhere the design thickness is 95 nm, therefore, the layer with athickness in the range of 86 nm to 105 nm can be used with no problem.Thus, a single antireflection layer is generally formed using a wetprocess such as fountain coating, die coating, spin coating, spraycoating, gravure coating, roll coating, and bar coating.

For example, the hard coat layer 6 is preferably made of a cured coatingfilm made of a curable resin such as a melamine resin, a urethane resin,an alkyd resin, an acrylic resin, and a silicone resin. The thickness ofthe hard coat layer 6 is preferably from 0.1 to 30 μm. If the thicknessis less than 0.1 μm, its hardness can be insufficient in some cases. Ifthe thickness is more than 30 μm, the hard coat layer 6 can be crackedin some cases, or the whole of the transparent laminated base substrate3 can curl in some cases.

The transparent conductive laminate A shown in FIG. 1 or 2 may beannealed in the range of 100 to 150° C., when a touch panel ismanufactured or as needed. Thus, the transparent conductive laminate Apreferably has heat resistance at 100° C. or higher, more preferably at150° C. or higher.

Next, a touch panel according to this embodiment is described below.FIG. 3 is a schematic cross-sectional view schematically showing a touchpanel according to this embodiment. Referring to the drawing, the touchpanel is configured to include the transparent conductive laminate A anda lower substrate A′ that are arranged opposite to each other withspacers s interposed therebetween.

The lower substrate A′ may comprise another transparent base substrate1′ and another conductive thin film 2′ laminated thereon. However, theinvention is not limited thereto, and, for example, the transparentconductive laminate A may also be used as the lower substrate A′.Basically, a glass plate or the same material as for the transparentlaminated base substrate 3 may be used as the material for forming thetransparent base substrate 1′. The thickness and so on of thetransparent base substrate 1′ may also be the same as those of thetransparent laminated base substrate 3. Basically, the same material asfor the conductive thin film 2 may be used as the material for formingthe conductive thin film 2′. The thickness and so on of the conductivethin film 2′ may also be the same as those of the conductive thin film2.

The spacers s may be of any insulating type, and various known spacersmay be used. There is no particular limitation on the method forproduction of the spacers s or the size, position or number of thespacers s. The spacers s may have any known shape such as asubstantially spherical shape and a polygonal shape.

The touch panel shown in FIG. 3 functions as a transparent switchsubstrate in which contact between the conductive thin films 2 and 2′ bytapping with an input pen or the like on the transparent conductivelaminate A side against the elastic force of the spacers s produces theelectrically ON state, while removal of the press turns it to theoriginal OFF state. In this structure, the touch panel is excellent inthe scratch resistance, pen input durability, surface pressuredurability, and the like of the conductive thin film 2 and thus canstably maintain the above function over a long period of time.

EXAMPLES

The invention is more specifically described with some examples below.It will be understood that the invention is not limited to the examplesbelow without departing from the gist of the invention. In each example,the term “part or parts” means part or parts by weight, unless otherwisestated.

Example 1 Formation of Transparent Conductive Thin Films

A 30 nm-thick undercoat layer (transparent dielectric thin film) of athermosetting resin (with a light refractive index n of 1.54) composedof a melamine resin, an alkyd resin and an organosilane condensate(2:2:1 in weight ratio) was formed on one side of a film substrate madeof a 25 μm-thick polyethylene terephthalate film (hereinafter referredto as “PET film”).

A 20 nm-thick first transparent conductive thin film (with a lightrefractive index of 2.0) of an indium-tin complex oxide was formed onthe undercoat layer by a reactive sputtering method using a sinteredmaterial composed of 95% indium oxide and 6% tin oxide in a 0.4 Paatmosphere composed of 95% by volume of argon gas and 5% by volume ofoxygen gas.

A 5 nm-thick second transparent conductive thin film of an indium-tincomplex oxide was formed on the first transparent conductive thin filmby a reactive sputtering method using a sintered material composed of90% indium oxide and 10% tin oxide.

After the first and second transparent conductive thin films were formedas described above, heat treatment was performed at 150° C. in acirculating hot air oven to crystallize both of the thin films so that astructure comprising the film substrate and the first and secondtransparent conductive thin crystalline films provided on one side ofthe film substrate was obtained.

(Formation of Hard Coat Layer)

A toluene solution as a material for forming a hard coat layer wasprepared by adding 5 parts of a photopolymerization initiator ofhydroxycyclohexyl phenyl ketone (Irgacure 184, manufactured by CibaSpecialty Chemicals Inc.) to 100 parts of an acrylic urethane resin(Unidic 17-806, manufactured by Dainippon Ink and Chemicals,Incorporated) and diluting the mixture with toluene to a concentrationof 30%.

The hard coat layer-forming material was applied to one side of a basefilm of a 125 μm-thick PET film and dried at 100° C. for 3 minutes. Thecoating was then immediately irradiated with ultraviolet light from twoozone-type high-pressure mercury lamps (each 80 W/cm² in energy density,15 cm focused radiation) to form a 5 μm-thick hard coat layer.

(Preparation of Transparent Laminated Base Substrate)

Subsequently, an about 20 μm-thick transparent acrylicpressure-sensitive adhesive layer with an elastic modulus of 10 N/cm²was formed on the other side of the base film opposite to the hard coatlayer-receiving side. The pressure-sensitive adhesive layer was formedusing a composition prepared by adding one part of an isocyanatecrosslinking agent to 100 parts of an acrylic copolymer of butylacrylate, acrylic acid and vinyl acetate (100:2:5 in weight ratio).Another base film of a 25 μm-thick PET film was bonded to thepressure-sensitive adhesive layer side so that a transparent laminatedbase substrate including the two PET films was obtained.

(Preparation of Transparent Conductive Laminate)

Under the same conditions as described above, a pressure-sensitiveadhesive layer was formed on the other side of the transparent laminatedbase substrate opposite to hard coat layer-receiving side, and thepressure-sensitive adhesive layer side was bonded to the film substrate(on the side where no conductive thin film was formed) so that atransparent conductive laminate according to this example was prepared.

Example 2

A transparent conductive laminated plate was prepared using the processof example 1, except that a sintered material composed of 97% by weightof indium oxide and 3% by weight of tin oxide was used instead in theprocess of forming the first transparent conductive thin film describedin the section “Formation of Transparent Conductive Thin Films” ofexample 1.

Example 3

A transparent conductive laminated plate was prepared using the processof example 1, except that in the process of forming the transparentconductive films described in example 1, a 200 nm-thick undercoat layerof a thermosetting resin (with a light refractive index n of 1.54)composed of a melamine resin, an alkyd resin and an organosilanecondensate (2:2:1 in weight ratio) was formed instead, and then a 30nm-thick SiO₂ film (with a light refractive index of 1.46) was formed bya silica coating method including the steps of diluting a silica sol(Colcoat P, manufactured by Colcoat Co., Ltd.) with ethanol to a solidconcentration of 2%, applying the diluted silica sol to thethermosetting resin layer, and then curing it after drying at 150° C.for 2 minutes.

Comparative Example 1

A transparent conductive laminate was prepared using the process ofexample 1, except that a transparent base substrate composed of the basefilm of a 125 μm-thick PET film and the hard coat layer formed thereon(without the base film of the 25 μm-thick PET film bonded in thetransparent laminated base substrate of example 1) was used in place ofthe transparent laminated base substrate.

Comparative Example 2

A transparent conductive laminate was prepared using the process ofexample 2, except that a transparent base substrate composed of the basefilm of a 125 μm-thick PET film and the hard coat layer formed thereon(without the base film of the 25 μm-thick PET film bonded in thetransparent laminated base substrate of example 1) was used in place ofthe transparent laminated base substrate.

(Preparation of Touch Panels)

The transparent conductive laminate obtained in each of the examples andthe comparative examples was used as one of the panel plates. A glassplate on which a 20 nm-thick transparent conductive thin film of made anindium-tin complex oxide (95% indium oxide and 5% tin oxide) was formedby the same method as described above was used as the other panel plate(lower substrate). Both panel plates were arranged opposite to eachother with 10 μm spacers placed therebetween in such a manner that thetransparent conductive thin films were opposite to each other, so that atouch panel for serving as a switch structure was prepared. Thetransparent conductive thin films on both panel plates were previouslyprovided with silver electrodes perpendicular to each other,respectively, before they were arranged opposite to each other.

(Refractive Index)

The refractive index was measured with a measuring beam incident on themeasurement surface of each object in an Abbe refractometer manufacturedby Atago Co., Ltd., according the measurement method specified for therefractometer.

(Thickness of Each Layer)

The thickness of the layer with a thickness of at least 1 μm, such asthe film substrate, the base film, the hard coat layer, and thepressure-sensitive adhesive layer, was measured with a microgauge typethickness gauge manufactured by Mitutoyo Corporation. The thickness ofthe layer whose thickness was difficult to directly measure, such as thehard coat layer and the pressure-sensitive adhesive layer, wascalculated by subtracting the thickness of the substrate from themeasured total thickness of the substrate and each layer formed thereon.

The thickness of the undercoat layer or the transparent conductive thinfilm was calculated using an instantaneous multichannel photodetectorsystem MCPD-2000 (trade name) manufactured by Otsuka Electronics Co.,Ltd., based on the waveform data of the resulting interference spectrum.

(Surface Resistance)

The surface resistance (Ω/square) of the ITO film in each touch panelwas measured using a two-terminal method.

(Light Transmittance)

Visible light transmittance was measured at a light wavelength of 550 nmusing a spectrophotometer UV-240 manufactured by Shimadzu Corporation.

(Reliability)

In a test of reliability at high temperature and high humidity, thesample was allowed to stand in an atmosphere at 85° C. and 85% RH for500 hours. The reliability at high temperature and high humidity wasevaluated by calculating a changing ratio of a surface resistance (R)after the test to a surface resistance (Ro) before the test (namelyR/Ro).

(Surface Pressure Durability)

As shown in FIG. 4, a surface pressure durability test tool (20 mmφ incontact diameter) was pressed against each touch panel under a load of 2kg (the coefficient of friction was from 0.7 to 1.3 when the tool was incontact with the touch panel), while the tool was allowed to slide oneach touch panel. After the sliding under specific conditions, linearitywas measured for an evaluation of surface pressure durability. Thesliding was performed on the transparent conductive laminate side in anarea at least 5 mm distant from the periphery of the touch panel. Thesliding was performed under the conditions of 100 times of sliding and atouch panel gap of 100 μm.

The linearity was measured as described below. Specifically, a voltageof 5 V was applied to the transparent conductive laminate, and thelinearity was obtained by the method below using the output voltageE_(A) at the measurement start point A, the output voltage E_(B) at themeasurement end point B, the output voltage E_(X) at the measurementpoint, and the theoretical value E_(XX).

Specifically, after the sliding on each touch panel, a voltage of 5 Vwas applied to the transparent conductive laminate, and the linearitywas obtained by the calculation using the output voltage E_(A) at themeasurement start point A, the output voltage E_(B) at the measurementend point B, the output voltage E_(X) at the measurement point, and thetheoretical value E_(XX) according to the mathematical expressionsbelow. FIG. 5 is a graph showing the relationship between the voltagevalue at the touch panel obtained in example 1 and the measurementpoint. In the graph, the solid line indicates actual measurement values,and the dotted line indicates theoretical values. The surface pressuredurability was evaluated from the resulting linearity value. The resultsare shown in table 1.

[Mathematical Expressions]

E _(XX)(theoretical value)=×(E _(B) −E _(A))/(B−A)+E _(A)

Linearity(%)={(E _(XX) −E _(X))/(E _(B) −E _(A))}×100

TABLE 1 First Transparent Second Transparent Conductive Thin ConductiveThin Transparent Base Film Film Substrate Evaluations SnO₂ SnO₂ Numberof Total Surface Visible Light Surface Content Thickness ContentThickness Laminated Thickness Resistance Transmittance ReliabilityPressure (wt %) (t₁: nm) (wt %) (t₂: nm) Base Films (μm) (Ω/square) (%)(R/R_(o)) Durability (%) Example 1 5 20 10 5 2 170 300 90 1.1 4 Example2 3 20 10 5 2 170 350 90 1.1 4 Example 3 5 20 10 5 2 170 300 91 1.1 2.5Comparative 5 20 10 5 1 125 300 90 1.1 8 example 1 Comparative 3 20 10 51 125 350 90 1.1 8 example 2

(Results)

It is apparent from table 1 that the transparent conductive laminate ofeach example satisfies high-temperature, high-humidity reliabilityrequirements for touch panels and also has high surface pressuredurability.

1. A transparent conductive laminate, comprising: a transparent filmsubstrate; a transparent conductive thin film provided on one side ofthe transparent film substrate; and a transparent base substrate bondedto another side of the transparent film substrate with a transparentpressure-sensitive adhesive layer interposed therebetween, wherein thetransparent conductive thin film comprises a first transparentconductive thin film made of an indium-tin complex oxide in whichSnO₂/(SnO₂+In₂O₃) is from 2 to 6% by weight and a second transparentconductive thin film made of an indium-tin complex oxide in whichSnO₂/(SnO₂+In₂O₃) is more than 6% by weight and not more than 20% byweight, the first and second transparent conductive thin films areformed in this order from the transparent film substrate side, thethickness t₁ of the first transparent conductive thin film and thethickness t₂ of the second transparent conductive thin film have thefollowing relationships: (1) t₁ is from 10 to 30 nm; (2) t₂ is from 5 to20 nm; and (3) the sum of t₁ and t₂ is from 20 to 35 nm, the firsttransparent conductive thin film and the second transparent conductivethin film are both crystalline films, and the transparent base substrateis a transparent laminated base substrate comprising at least twotransparent base films laminated to one another with a transparentpressure-sensitive adhesive layer interposed therebetween.
 2. Thetransparent conductive laminate according to claim 1, further comprisinga transparent dielectric thin film through which the transparentconductive thin film is formed on the film substrate.
 3. The transparentconductive laminate according to claim 1, wherein the transparentconductive laminate further comprises a resin layer provided on theouter surface of the transparent base substrate.
 4. A touch panel,comprising the transparent conductive laminate according to claim 1.